The instant application should be granted the priority dates of Jan. 28, 2006, the filing date of the corresponding German patent application 10 2006 004 068.6 as well as Jan. 26, 2007, the filing date of the International patent application PCT/EP2007/000689.
The present invention relates to a method of mixing at least one fluid stream with a large gas stream, especially for introducing a reducing agent into a flue gas that contains nitrogen oxides, and also relates to an apparatus for mixing at least one fluid stream with a large gas stream that flows in a gas duct, especially for introducing a reducing agent into a flue gas that contains nitrogen oxides.
EP 1 604 742 A1 discloses such a method in conjunction with electric filters for the dust separation of large gas streams, according to which the flow whirl, which is formed at the inclined mixer disk, is designated as a leading edge whirl. The edge of the preferably circular disk that is directed against the large gas stream is designated as the intake edge and the other edge is designated as the breaking edge. These are not linear edges but rather curved edges.
The vertical wall of the gas duct that guides the large gas stream has a short section of pipe for the admixture of a conditioning fluid passed perpendicularly therethrough. The short pipe section opens out, as viewed in the direction of flow of the large gas stream, behind the intake edge of the mixer disk without overlapping the mixer disk. The laminar conditioning agent stream that exits the short pipe section strikes the edge-continuous partial surface of the discharge side of the mixer disk, adjacent to the section outlet, at an angle that corresponds to the angle of inclination of the disk relative to the direction of flow of the large gas stream.
With this procedure, the conditioning agent is not optimally mixed into the whirl system that results at the mixer disk.
Column 6, lines 5-6, of EP 1 604 742 A1 indicates that methods are also expedient according to which the admixture device is mounted directly on the whirl apparatus.
U.S. Pat. No. 5,356,213 A, in conjunction with a gas phase oxidation process in the petrochemical field, discloses a method of mixing a small gas stream, e.g. oxygen, with a large gas stream, e.g. air, according to which the oxygen, in at least two swirled partial streams, is introduced into the air stream, which flows essentially undisturbed in a duct, via radially extending swirl vanes disposed on the end of a tubular section that opens in the direction of flow of the air, whereby the velocity of the oxygen is increased upstream of the swirl vanes and a cloth is stretched over the outlet end of the tubular section downstream of the swirl vanes.
With the mixing device described in EP 1 166 861 B1, in conjunction with Denox units and electric filters, the mixer disk (built-in surface) has a chamber into which leads a separate flow channel for the fluid that is to be admixed and which serves as a distribution chamber for the fluid stream. The chamber is provided on the back side (discharge side; lee side) of the mixer disk that faces away from the in-flow of the large gas stream with discharge openings from which exit in a laminar manner partial streams of the fluid stream, and is disposed in the region of the intake edge. Adjoining the distribution chamber toward the breaking edge are chambers that, however, have no distribution function nor a flow-related function, but rather serve exclusively for the reinforcement of the mixer disk. The discharge openings can be formed in the cover of the distribution chamber or in the side wall thereof. However, they can also be formed in an additional hood that is placed upon the chamber. It is furthermore possible that the chamber itself not be provided with a cover that is parallel to the mixer disk, but rather itself have a hood-shaped configuration. The flow channel for the supply of fluid can enter from the windward side of the mixer disk through the disk, or can be guided to the distribution chamber on the lee side of the mixer disk. With the method described in EP 1 166 861 B1 an additional chamber is required and the mixing-in is again effected only in the vicinity of the intake edge.
Such methods, designated as mixing methods having a static mixer, are, for example, also used with SCR units, to reduce the NOx level (Selective Catalytic Reduction) of flue gases, for example of power plant furnaces, by means of reducing agent and catalyzer. In this connection, it is customary, where the reducing agent is NH3, that it is stored in the form of pressure-condensed NH3 or of ammonium hydroxide (NH4OH), and pre-vaporized NH3 is sprayed into the flue gas stream via a carrier gas stream and is mixed with the flue gas stream. Where the reducing agent is urea, first an aqueous urea solution is produced that, after suitable processing, is then sprayed into the flue gas stream in gaseous form.
The methods are furthermore used, for example, for industrial chimneys, spray driers (See e.g. EP 0637 726 B1), heat exchangers, flue desulfurization units, and hybrid cooling towers.
It is an object of the present invention, for the method and the apparatus of the aforementioned general types, to improve the mixing of the fluid stream into the large gas stream.